In general, in an image forming apparatus of an electrophotographic system, plural photoconductive drums are arranged in parallel and laser beams are irradiated on the respective photoconductive drums to form electrostatic latent images. Toner images of respective colors are formed on the photoconductive drums by developing devices. The toner images of the respective colors are multiply transferred onto a sheet to obtain a color image.
The developing devices are provided in the plural photoconductive drums, respectively. Plural toner cartridges for supplying toners to the developing devices are attached to carry the toners stored in the toner cartridges to the developing devices.
Sub-tanks may be arranged between the toner cartridges and the developing devices. The sub-tanks are generally called sub-hoppers and are auxiliary toner tanks provided between the toner cartridges and the developing devices. Since the toners in the toner cartridges are supplied to the sub-hoppers, it is possible to perform printing using the toners in the sub-hoppers even if the toners in the toner cartridges are exhausted.
JP-A-11-24513 discloses a toner supplying apparatus. In an example of the structure disclosed in JP-A-11-24513, sub-hoppers are arranged between toner cartridges and developing devices.
In the image forming apparatus in the past, it is necessary to feed developers into the developing devices when the image forming apparatus is set up. During the setup, the toner cartridges are replaced with toner cartridges containing the developers to supply the developers to the developing devices. Therefore, work for feeding the developers during the setup is complicated.
The toner cartridges tend to have larger capacities. It is evident that toner quantities in the toner cartridges are large compared with necessary quantities of the developers. When the developers are stored in the toner cartridges, developer cartridges increased in size have to be used.
When the sub-hoppers are replaced, since there are the plural sub-hoppers, it is likely that the respective sub-hoppers are mounted in wrong positions.